1. Field of the Invention
The present invention relates to a method for manufacturing an acoustic vibration plate for use in a speaker device or the like.
2. Prior Art
Metal titanium has been being widely used for acoustic vibration plates used in speakers or the like, since it has a small volume density and a large elastic modulus. In recent years, a proposal has been made for an acoustic vibration plate in which titanium oxide having a better characteristic than metal titanium is coated on the surface of metal titanium, to improve much more the acoustic characteristic of an acoustic vibration plate.
For example, Japanese Patent Application Laid-Open Publication No. 51-12130 proposes a speaker vibration plate obtained by forming a titanium oxide (TiO2) layer on the surface of metal titanium in an argon atmosphere containing oxygen. In addition, Japanese Patent Application Laid-Open Publication No. 2-152399 proposes a vibration plate for a speaker in which a titanium oxide layer having a film thickness of 20 to 200 nm or a film thickness of 1 xcexcm or more is formed on the surface of metal titanium by an anode oxidation method. The acoustic vibration plate obtained by forming a titanium oxide layer on the surface of metal titanium, as described above, has a higher rigidity in comparison with an acoustic vibration plate made of only metal titanium, so it has an excellent acoustic characteristic.
In addition to acoustic vibration plates using metal titanium, proposals have been made for an acoustic vibration plate using ceramics such as SiC or the like. Like the acoustic vibration plate using metal titanium, the acoustic vibration plate has a high rigidity, so it has an excellent acoustic characteristic. Considered as methods for preparing a vibration plate of this kind are a method of depositing ceramics such as SiC or the like in a shape like a vibration plate by a CVD method or the like, and a method of mixing and molding black lead and resins into a shape like a vibration plate and of thereafter sintering them to ceramic-carbonize the entire resultant.
However, the vibration plate as described above which is prepared by forming a titanium oxide layer on the surface of metal titanium has a very thin titanium oxide layer, compared with the thickness of metal titanium as a base material. Therefore, the acoustic characteristic of the vibration plate is not so improved as expected from the original excellent characteristic of titanium oxide itself.
Also, the method of preparing a vibration plate by depositing ceramics such as SiC or the like requires an expensive apparatus for preparing a thin film, such as a CVD apparatus or the like. Since this kind of thin-film preparation apparatus cannot process a large quantity of vibration plates together at once, the productivity is low so that the manufacturing cost is increased. In addition, it is difficult to prepare a vibration plate having a complicated shape by the method of mixing and ceramic-carbonizing black lead and resins to prepare a vibration plate.
Hence, the present invention has been proposed in view of the situation of the prior art as described above, and has an object of providing a method capable of manufacturing an acoustic vibration plate with a completed shape at low costs, which can provide an excellent reproducing characteristic within a high-frequency tone range when used in a speaker.
To achieve the above object, a method for manufacturing an acoustic vibration plate according to the present invention comprises: a molding step of molding metal titanium into a shape of an acoustic vibration plate, to obtain a titanium vibration plate; and a ceramic-formation step for performing a heat treatment on the titanium vibration plate, thereby to change entirely the titanium vibration plate into titanium oxide.
In the above-described method for manufacturing an acoustic vibration plate, according to the present invention, metal titanium which has excellent processability is molded into the shape of the acoustic vibration plate thereby to prepare a titanium vibration plate, in the molding step. Next, in the ceramic-formation step, a heat treatment is carried out thereby changing the entire of the titanium vibration plate into titanium oxide. Therefore, an acoustic vibration plate which has a small volume density and a high elastic modulus can be manufactured in a desired shape.